1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method and, more particularly, semiconductor device manufacturing method of providing copper wirings.
2. Description of the Prior Art
In the step that copper wiring is formed in a semiconductor device, a method of embedding copper into the groove formed in the insulating film has been employed.
As the method of embedding the copper into the groove, there are the method of forming the copper film in the groove by using sputtering, the method of growing the copper film on the insulating film and in the groove by using plating or chemical vapor deposition, etc. In the case of sputtering, since a concave portion is formed on the upper surface of the copper film over the groove, the method of planarizing the upper surface of the copper film by reflowing the copper film is employed.
Also, it has been recorded in Patent Application Publication (KOKAI) Hei 4-217386 that, after the first copper film has been formed on the insulating film and in the groove by using sputtering, the second copper film is formed on the first copper film by virtue of electroplating while using the first copper film as the electrode.
The copper film being formed by any method is removed from the upper surface of the insulating film by virtue of CMP (chemical mechanical polishing) to be remained only in the groove. Then, the copper film remaining along the groove is used as the wiring.
According to the sputtering method, the copper film is easy to grow in the vertical direction of the substrate but is difficult to grow in the lateral direction of the substrate. As a consequence, there has been such a tendency that the copper film formed along the inner periphery of the groove of the insulating film becomes thinner while the copper film formed on the bottom of the groove and the upper surface of the insulating film becomes thicker.
Therefore, a concave portion occurs on the surface of the copper film over the groove. If the copper film is polished by chemical mechanical polishing in the situation that such groove remains as it is, wiring resistance is increased since groove or dishing is generated in the copper film which has remained in the groove. This is because such chemical mechanical polishing is attended with chemical reaction, so that the concave portion cannot be eliminated. In this case, even if the copper film is heated to reflow, the concave portion does not sufficiently disappear.
In contrast, according to the electroplating method, a cavity is ready to occur in metal which has been grown in the groove as an aspect ratio of the groove becomes higher, whereby higher resistance is caused in the groove. Such problem has been reported in Patent Application Publication (KOKAI) Hei 6-326055.
In addition, the copper film which is formed by the plating or the chemical vapor deposition has insufficient electromigration resistance to thus reduce reliability of the wiring.
Besides, as set forth in Patent Application Publication (KOKAI) Hei 4-217386, according to the method in which the second copper film is embedded into the groove by plating immediately after the first copper film is formed along the inner surface of the groove by sputtering, since a shape of the groove is substantially reflected on a shape of the first copper film, the cavity which is the defect of the plating method is ready to occur with the increase in the aspect ratio.